This invention relates to a method for accurately depositing a conductive coating of predetermined thickness on a substrate, and particularly to such a method wherein the simultaneous deposition of a conductive coating of the predetermined thickness on a substrate and on a measuring body causes an abrupt change in resistance of the measuring body which is utilized to terminate the deposition.
It is often necessary to deposit a conductive coating of an accurately predetermined thickness on a substrate, as by deposition under vacuum, with such deposition being reproducible with a high degree of accuracy. Heretofore, various methods have been employed to control the thickness of a coating deposited on a substrate. Most of the methods include determining the added mass or weight on the substrate and then calculating the thickness, e.g., weighing the substrate before and after the deposition or employing a pair of quartz crystals and determining the added mass from the change in resonant frequency. Another method utilizes two spaced apart conductive regions each of which is connected to a resistance measuring device. As the deposition of the conductor proceeds, the space is gradually filled with conductive material causing the resistance to decrease proportionally to the thickness of the coating and the particular conductive material employed.
Although available methods are suitable for most situations, present methods generally involve lengthy calculations as the thickness of the coating is measured indirectly. Furthermore, the indirect measurement of thickness increases the likelihood of error while decreasing the accuracy obtainable. In addition, present methods often require the use of costly equipment and continuous monitoring so as to be unacceptable to many users.